1. Field of the Invention
The present invention relates to a liquid curable resin composition. More particularly, the present invention relates to a liquid photo-curable resin composition which upon radiation produces cured products which exhibit superior heat resistance, excellent mechanical strength, and superb adhesive characteristics. The composition is suitable as a photo-curable adhesive, a photo-curable sealing material, a resin for optical three-dimensional molding, and a coating material for optical fibers, optical fiber ribbon matrix, and the like.
2. Description of Prior Art
Among photo-curable resin compositions, acrylate-based resin compositions have been developed as a material with characteristics suitable for a variety of applications by blending urethane acrylate as a major component of acrylate monomers. On the other hand, epoxy-based photo-curable resin compositions are used for applications making good use of the excellent adhesive properties and the high heat resistance of the epoxy resin.
A coating material for optical fibers is one specific application of photo-curable resins. As the use of optical fiber cables advances, higher durability is demanded of the coating material. Specifically, there is a problem wherein coloring of the optical fiber coating materials may be so detonated due to poor durability of the coating material that it becomes difficult to differentiate one optical fiber cable from another with a different color by sight. This may cause problems in the maintenance of optical fiber cables. Deterioration in color visibility has been confirmed to be caused not only by the discoloration of the bundling materials, but also by the discoloration of the primary and secondary coating that cover the individual optical fibers.
High adhesive properties and superior durability sufficient to prevent discoloration are demanded for photo-curable adhesives depending on the application. In addition, optical characteristics must not change in adhesives used for glass lenses and adhesives used to join quartz glass and optical fibers.
Urethane acrylate-based materials used in photo-curable resin compositions which are used for a variety of applications are flexible materials possessing superior mechanical characteristics such as high tenacity. Epoxy-based materials, on the other hand, are used for applications requiring the excellent characteristics of the epoxy resin, such as high adhesive properties and superior heat resistance.
However, the epoxy-based materials possess inadequate tenacity, while the urethane acrylate-based materials lack heat resistance. There are no known materials which possess both the characteristics possessed by these two types of resin materials.
Accordingly, an object of the present invention is to provide a liquid curable resin composition which undergoes the least change in characteristics when exposed to heat and light, maintains its transparency or is more resistant to coloration, exhibits superior mechanical characteristics and excellent adhesive properties. Such a resin composition is preferably formulated as to be suitable as a photo-curable adhesive or a coating material for optical fibers.